El manto Iítosférico en el sureste de España: Aportaciones de los xenolitos englobados en rocas alcalinas del mioceno-plioceno

Abstract

Pliocene-Quaternary nephelinitic and alkali basaltic lavas and pyroclastic deposits from Cofrentes and Tallante and Miocene lamproitic lavas from Aljorra host xenoliths and megacrysts of lithospheric mantle origin. The xenolith suite consists of spinel Iherzolites and harzburgites and with protogranular, porphyroclastic and equigranular or transitional (protogranular to porphyroclastic) textures. The textural features provide evidence of ductile-brittle deformation of Tallante xenoliths, whose mineralogy and mineral chemistry data (presence of kaersutite and phlogopite) also bear evidence of fluid-induced metasomatism of the lithospheric mantle. P-T estimates suggests that mostly protogranular xenoliths are reliable to define a palaeogeotherm, which is from 950-1185°C at 2,5-3.0 CPa, 794-805°C and 1,7-7,3 CPa for Cofrentes to 936-958°C, at 1,1 -1,2 CPa for Tallantes. The Aljorra peridotite suggests a temperature of ~880°C and a pressure of ~1,8 GPa. The picture of equilibrium P-T conditions indicates that the differences in the mantle lithosphere composition is related to (1) its deformation state and (2) metasomatic events, but also to (3) the location of entrapment during magma ascent in the lithosphere generated by diapiric uprising of asthenospheric mantle. The location of the entrainment is either close to the magma generation area or is situated at the mantle-crust boundary